fix: be explicit on used generic types and lifetimes

examples/sliding-puzzle.rs

@@ -95,7 +95,7 @@ impl Game {
     // However, since the successors are the current board with the hole moved one
     // position, we need to build a clone of the current board that will be reused in
     // this iterator.
-    fn successors(&self) -> impl Iterator<Item = (Game, u8)> {
+    fn successors(&self) -> impl Iterator<Item = (Game, u8)> + use<> {
         let game = self.clone();
         SUCCESSORS[self.hole_idx as usize]
             .iter()

src/grid.rs

@@ -214,7 +214,7 @@ impl Grid {
 
     /// Return an iterator over the border vertices. The grid must not have
     /// a zero width or height.
-    fn borders(&self) -> impl Iterator<Item = (usize, usize)> {
+    fn borders(&self) -> impl Iterator<Item = (usize, usize)> + use<> {
         let width = self.width;
         let height = self.height;
         (0..width)

src/matrix.rs

@@ -531,7 +531,7 @@ impl<C> Matrix<C> {
         &self,
         (r, c): (usize, usize),
         diagonals: bool,
-    ) -> impl Iterator<Item = (usize, usize)> {
+    ) -> impl Iterator<Item = (usize, usize)> + use<C> {
         let (row_range, col_range) = if r < self.rows && c < self.columns {
             (
                 r.saturating_sub(1)..(self.rows).min(r + 2),
@@ -597,7 +597,7 @@ impl<C> Matrix<C> {
         &self,
         start: (usize, usize),
         direction: (isize, isize),
-    ) -> impl Iterator<Item = (usize, usize)> {
+    ) -> impl Iterator<Item = (usize, usize)> + use<C> {
         in_direction(start, direction, (self.rows, self.columns))
     }
 
@@ -628,14 +628,14 @@ impl<C> Matrix<C> {
         since = "4.1.0",
         remove = "> 4.x"
     )]
-    pub fn indices(&self) -> impl Iterator<Item = (usize, usize)> {
+    pub fn indices(&self) -> impl Iterator<Item = (usize, usize)> + use<C> {
         self.keys()
     }
 
     /// Return an iterator on the Matrix indices, first row first. The values are
     /// computed when this method is called and will not change even if new rows are
     /// added before the iterator is consumed.
-    pub fn keys(&self) -> impl Iterator<Item = (usize, usize)> {
+    pub fn keys(&self) -> impl Iterator<Item = (usize, usize)> + use<C> {
         let columns = self.columns;
         (0..self.rows).flat_map(move |r| (0..columns).map(move |c| (r, c)))
     }

tests/pathfinding.rs

@@ -4,7 +4,7 @@ mod ex1 {
     use pathfinding::prelude::*;
 
     #[allow(clippy::trivially_copy_pass_by_ref)]
-    fn successors(node: &u8) -> impl Iterator<Item = (u8, usize)> {
+    fn successors(node: &u8) -> impl Iterator<Item = (u8, usize)> + use<> {
         lazy_static! {
             static ref SUCCESSORS: Vec<Vec<(u8, usize)>> = vec![
                 vec![(1, 7), (2, 7), (3, 6)],